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Homework Help: Input math problem

  1. Dec 26, 2005 #1
    y`` +y`+y=r(t)
    why's r(t) the input and not t?
  2. jcsd
  3. Dec 26, 2005 #2
    Because the right hand side of that equation denotes a function of t.

    r(t) could be t but it can also be every other function that depends on t.

    Basically, r(t) is the most general form to denote "a function of t"

  4. Dec 26, 2005 #3


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    Science Advisor

    That's not really mathematics- it's "Engineer speak".

    From the point of view of an Engineer, a differential equation is a machine to which you supply an "input" and get an "output". The differential operator y"+ y'+ y is the machine. Whatever function you have on the right hand side is the "input" (which varies with t) and y(t) satisfying the equation is the "output".

    (Edited- thanks, Marlon.)
    Last edited by a moderator: Dec 27, 2005
  5. Dec 26, 2005 #4
    The differential operator is not y''+y' but y''+y'+y

  6. Dec 28, 2005 #5
    thank you very much!!!
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